UK households would have to pay three times as much as their North American counterparts for a family pack of Vista, Microsoft's new operating system.

Microsoft has admitted it is selling upgrade versions of Home Premium for $50 (£25) each to households in the US and Canada when they buy an upgrade or full copy of Vista Ultimate.

The $50 per Vista Home Premium deal on Microsoft's website is billed as a 'Family Discount' and represents a 60 per cent saving over US retail prices. By comparison the UK Vista Home Premium upgrade price is £149.99.

The family discount means upgrading a three-PC home in the US costs £185, whereas UK families will have to stump up £550 to do the same, based on a one Ultimate upgrade, two Home Premium upgrade package. The deal only allows for two copies of Home Premium to be bought.

Microsoft told PCW that the discount is a time-limited trial, provisionally ending on the 30 June 2007. After that the scheme may be extended to other territories.

Consumer outrage at the high Vista pricing is growing and a petition on the 10 Downing Street website has been signed by over 600 people within days of going live. The petition gives disgruntled users until 20 April 2007 to register their anger at the high price to the Prime Minister.

The Office of Fair Trading, the Department for Trade and Industry and the National Consumer Council, which represent UK business and consumer interests, all refused to comment on Microsoft's Vista pricing.

The move is another blow to customers after Microsoft started selling Windows Vista for 60 per cent more in the UK that the US. In a BBC interview, Bill Gates blamed the high price on exchange rates.

See also:
Four copies of Vista get you a free trip to the US
Vista Express Upgrade programme crashes
Review: Microsoft Windows Vista operating system